This invention relates to a process of measuring the side-reading of abutted-junction read heads for magnetic storage devices, and particularly to measuring the width of abutted-junction magnetoresistive and giant magnetoresistive heads.
Magnetoresistive (MR) and giant magnetoresistive (GMR) heads are employed in magnetic storage devices to read data recorded in a recording medium, such as a rotating disc. Data are recorded as transitions in magnetic domain orientations in the recording medium so that as the medium moves past the head, the transitions in magnetic orientation causes transitions in magnetic flux to the head. Transitions in magnetic flux in the head causes changes in the electrical impedance of the MR or GMR element. The changes in the electrical impedance are detected by applying a bias current through the head and detecting changes in the voltage across the head. Consequently, the changing voltage across the head is representative of the data recorded on the magnetic medium.
MR heads employ a magnetoresistive layer whose resistance changes with transitions in external magnetic fields from data on the passing magnetic recording media. GMR heads employ a stack of at least three layers, namely a ferromagnetic active or free layer, a ferromagnetic pin layer and a nonmagnetic spacer layer sandwiched between the two ferromagnetic layers. The direction of magnetization in the pin layer is held constant while the magnetization in the active or free layer is permitted to rotate in response to the external magnetic field. The GMR element is sometimes called a spin valve due to the rotation of magnetization in the free layer. The resistivity of the stack varies as a function of the angle between the magnetization of the free or active layer and the magnetization of the pin layer. Contact layers are attached to the MR element or GMR stack to supply bias current to the element or stack to permit measurement of resistance.
Many MR and GMR heads employ permanent magnets abutting opposite sides of the magnetoresistive element or stack. These heads are referred to as xe2x80x9cabutted-junctionxe2x80x9d MR and GMR heads. Usually, the head is formed by forming the element or stack on a planar lower shield and thereafter forming the permanent magnet and contact layers. The height configurations of the permanent magnet and contact layers often require that an upper shield, opposite the lower shield, be of varying distance from the lower shield. More particularly, the height of the permanent magnet and contact layers together is often greater than the height of the MR layer or GMR stack, so the portion of the upper shield over the permanent magnet and contact layers is at a greater distance from the lower shield than the portion of the upper shield over the MR or GMR. Moreover, due to the tapered junction between the permanent magnet and the MR element or GMR stack, some portions of the element or stack are wider across the track width of the head than other portions of the element or stack.
Many magnetic heads respond to changing magnetic fields outside the bounds (width) of the head. This effect, called a xe2x80x9cside-readingxe2x80x9d effect, is a source of noise in the recovered data signal, and a source of cross-talk, a phenomenon where the read head reads data from two or more adjacent tracks.
At least two factors contribute to side-reading in abutted-junction heads. First, the flux density of the magnetic field created by the data on the recording media is greatest when the head is centered on the track. The recording tracks are usually wider than the read head width, so that when the head is centered on a track, magnetic flux from portions of the track beyond the width of the transducing read gap (the width of the MR or GMR element, for example) are read. Read heads are designed such that the length of the transducing read gap (in the direction of track length) is a little more than the minimum spacing between successive transitions along the track. By limiting the length of the transducing gap, two or more successive transitions are not read simultaneously as to cancel each other out. However, in abutted-junction read heads, the spacing between the top and bottom shields increases (along the track length) outside the width of the head, resulting in plural transitions between the shields outside the head width and a canceling effect on the read signal. Second, in abutted junction GMR heads, the active or free layer of the stack extends outside the effective width of the read head due to the tapered abutted-junction structure. This extended portion of the active or free layer extends into the contact region where shield-to-shield spacing is greater, thus increasing side-reading.
Areal data density for a magnetic media is the product of the bit density along the length of the recording tracks and the density of those tracks in a direction normal to the track length. As track density increases, track width and spacing decreases and areal density increases. However, smaller track widths and spacing requires read heads with more narrow widths. As track spacing becomes smaller, the effects of side-reading in read heads becomes more critical. The effects of side-reading in read head is a limiting factor on the spacing between adjacent tracks, and hence a limiting factor to increased areal density.
Considerable research is being conducted into the design of read heads to minimize the effective width of the head. One factor in that research is the minimization of side-reading of heads. However, there has been no effective technique for measuring side-reading in a head. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention is directed to measuring the side-reading of an abutted-junction transducer, such as a magnetoresistive or giant magnetoresistive read head. The transducer is moved relative to at least one microtrack having a selected transition density. A plurality of positions of the transducer are identified relative to the at least one microtrack where the transducer provides a predetermined response. The side-reading distance of the transducer is identified from the plurality of positions.
In one embodiment, a plurality of microtracks are constructed during respective iterations, each microtrack having a different transition density. The positions of the transducer are identified during each iteration relative to the respective microtrack where the transducer provides the predetermined response.
In another embodiment, the selected transition density has a fundamental frequency. The positions of the transducer are identified relative to the microtrack where the transducer provides the predetermined response at each of a plurality of harmonic frequencies of the fundamental frequency.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.